The thought of marrying her out of the blue seems a bit much?
...Such a good girl like her? I don't see the problem at all.
Great ending though. 'Daddy', eh? That'd certainly be nice. Who knows? He may already have become one.

Well, being told to marry a girl out of the blue can be a bit much. And even if she's beautiful and clearly likes him, I could totally see the guy being reluctant to jump straight to marriage without even really dating first. Marriage is not a small commitment (especially for someone as young as he seems to be). But if he just wants to go slowly and date her first rather than jumping straight to marriage, he should make that clear up front rather than pseudo-rejecting her like he seems to have been doing. That could really hurt the girl's feelings and make her think that he dislikes her (which happens often enough with situations like this in hentai). But of course, since this is hentai, she jumps his bones and wins him over - and most of these sort of stories seem to go with either the girl being aggressive or the guy just not being able to contain his lust anymore (much to her relief/delight). Either way, you usually get a nice, vanilla ending out of it.